In recent years, human-computer interaction systems that are constituted with electronic pens, various sensors, projectors, and the like, or what is called “interactive white boards” have been proposed (see, e.g., Patent document 1).
In an interactive white board using an electronic pen, a movement trajectory of the electronic pen on a board plane is detected by a sensor, and drawn figures and characters are displayed on the board plane. Also, a command to a computer is recognized from lines of movement of the electronic pen on the board plane, by which an operation of the computer is controlled.